MEMS gas preconcentrator filled with CNT foam for exhaled VOC gas detection

For disease monitoring and diagnostics using breath analysis, the gas preconcentrator is crucial for low-concentration exhaled volatile organic compound (VOC) gas analyses, and overcomes existing detection limits associated with the commercialized gas sensors. In this work, the microelectromechanical system (MEMS) gas preconcentrator chip was designed and fabricated for conducting low-power-operated breath analyses. It consists of a microheater and a gas chamber filled with a carbon nanotube (CNT) foam. The CNT foam, used as a gas adsorbing material, has several advantages including its large gas adsorption capacity due to its large surface-to-volume ratio, a low pressure drop due to its high porosity, and a rapid thermal desorption due to its high thermal conductivity. Using the developed MEMS gas preconcentrator chip, several basic performances were tested for clinically important VOC gases using a commercial gas chromatography-flame ionization detector (GC-FID). For gas preconcentrations over five minute interval, the preconcentration factors for methane and ethane gases were 8.05 and 7.72, respectively. These results suggest that the developed MEMS gas preconcentrator can be potentially utilized to analyze the low-concentration exhaled VOC gases for the purpose of noninvasive medical diagnoses.